Brillouin spectroscopy is an inelastic light scattering technique that allows for accurate measurement of high frequency longitudinal and transverse sound velocities within materials. Determination of sound velocity and acoustic attenuation further permits the determination of bulk mechanical properties including the elasticity, the bulk modulus, the Laudau-Placzek ratio, refractive index, and the Poisson's ratio. Historically, scanning Fabry-Perot Interferometer Brillouin spectroscopy of liquid and solid materials has been very difficult to measure and has required humidity and temperature stability for the duration of the experiment, which can be many hours. This is the one reason for its obscurity and the dominance of other types of elastic measurements such as ultrasonics and stress-strain techniques. Our group plans to make Brillouin spectroscopy a more utilized spectroscopy by creating a much faster and easier to use Brillouin spectrometer that allows performance of both microscopy and imaging techniques. It has recently been shown that advents in optical technologies can be used to design an easy-to-use and fast collecting angle dispersion type Fabry-Perot interferometer. The design of an angle-dispersive confocal Brillouin instrument will allow the acoustic properties of most materials to be obtained in a few milliseconds to seconds. Our group proposes to develop an angle dispersion type Fabry-Perot interferometer based Brillouin spectrometer with microscopy and imaging capabilities. This proposed instrument will be the first of its kind and will open the doors to new types of in-situ non-destructive mechanic measurements and mechanical contrast imaging.
Many of the methods currently used to determine the mechanical properties of a material result in destruction of the original material. Brillouin spectroscopy methods can, however, be used to gauge both the 'hardness' of a material as well as the elasticity in a nondestructive manner. Named after its discoverer, Marcel Brillouin, it is among the most powerful methods of revealing the dynamical and mechanical properties associated with materials. Brillouin spectroscopy directly measures the frequency shift in laser light impinging on a solid or liquid sample (similar to police radar that use a frequency shift to measure speed). This allows the determination of many mechanical properties including the elasticity (stiffness), the bulk modulus (compressibility) and refractive index. J.L. Yarger's research group has recently developed an angle-dispersive Fabry-Perot interferometer (ADFPI) for use in Brillouin spectroscopy. We propose using the recently designed ADFPI as the bases for constructing a confocal Brillouin microscopy and imaging system to extend the imaging and spectroscopy techniques available for characterization of the mechanical and elastic properties of materials.
